The present invention relates to an optical disk apparatus, and more particularly to an optical disk apparatus for detecting a TE balance correction value to be an offset voltage for setting an amount of a shift of a TE balance to be zero and a detrack correction value to be an offset voltage for obtaining the highest signal quality of an output of an optical pickup.
In an apparatus for reproducing data recorded on an optical disk, the following technique has been proposed in order to enhance precision in a tracking servo and to improve the signal quality of a reproducing signal (which will be referred to as a first related art). More specifically, in the technique, focus-ON is carried out by executing a servo control of focusing and track-ON is carried out by executing a servo control of tracking as shown in FIG. 12. In this state, there is carried out a defocus regulation for adding an offset voltage to a focus error signal (which will be hereinafter referred to as an FE signal) in such a manner that a jitter amount of an RF signal is a minimum (an amplitude of the RF signal is a maximum). Then, a tracking servo is turned OFF and an offset voltage is added to a tracking error signal (which will be hereinafter referred to as a TE signal) obtained when a beam spot crosses a track in such a manner that a central voltage of the TE signal is equal to a reference voltage, that is, an amount of a shift of a balance of the TE signal (which will be hereinafter referred to as a TE balance) is zero. When the amount of a shift of the TE balance is set to be zero, the most stable tracking servo can be obtained. Also in the case in which a recording plane of the optical disk has scratches and dirt, subsequently, the tracking is carried out without causing a shift (for example, see JP-A-2000-76668).
Moreover, the following technique has been proposed (which will be referred to as a second related art). More specifically, in the technique, an offset voltage (to be added to a TE signal) for setting an amount of a shift of a TE balance to be zero which is generated when an objective lens of an optical pickup is shifted by a predetermined amount is calculated and stored at time of a boot in which an initialization is to be carried out. When a seeking operation is to be carried out over a target track, furthermore, an amount of a shift of the objective lens is calculated during the seeking operation. Then, the offset voltage for setting, to be zero, the amount of a shift of the TE balance obtained when it reaches the calculated amount of a shift, is calculated by referring to an offset voltage which is stored, and the offset voltage thus calculated is added to the TE signal. When a servo control of tracking is restarted after the seeking operation, accordingly, the most stable tracking can be carried out. Therefore, track-ON is reliably carried out so that precision in the seeking operation can be enhanced (for example, see JP-A-2004-326910).
Furthermore, the following technique has been proposed (which will be referred to as a third related art). More specifically, in the technique, the offset voltage for setting the amount of a shift of the TE balance to be zero is added to the TE signal when a jump mode is brought, and an offset voltage having a jitter and an error rate minimized is added to the TE signal when a mode following a track (a mode for carrying out a reproduction) is brought. Accordingly, it is possible to carry out a stable track jump and a reproduction having a low error rate (for example, see JP-A-2005-71545).
In the case in which the first related art is used, however, the following problem arises. More specifically, in an apparatus for generating a TE signal by a DPD method, in the case in which a CD is reproduced (mainly a CD-R or a CD-RW), there are some apparatuses in which an amount of a shift (an amount of detrack) from a central position of a track of a beam spot is increased due to a shift of an attachment position of a PDIC that is a device for detecting a reflected light and a variation in a sensitivity of a region of the PDIC which is divided into four parts also when the offset voltage for setting the amount of a shift of the TE balance to be zero is added to the TE signal. When the CD is reproduced by using an apparatus in which the amount of detrack is increased, the jitter is increased. Consequently, there is a problem in that an error rate is reduced and the signal quality of a reproduction is deteriorated.
Referring to the second related art, the offset voltage for setting the amount of a shift of the TE balance to be zero is varied depending on the amount of a shift of the objective lens. Consequently, the offset voltage corresponding to the amount of a shift is calculated and is added to the TE signal so that a stability of tracking after a seeking operation can be maintained. For this reason, the second related art is hard to apply in respect of the solution of the problem in the first related art.
Referring to the third related art, the offset voltage for setting the amount of a shift of the TE balance to be zero is added to the TE signal when the jump mode is brought, and the offset voltage having a jitter and an error rate minimized is added to the TE signal when a mode following a track (a mode for carrying out a reproduction) is brought. For this reason, the technique is hard to apply in respect of the solution of the problem in the first related art.